Multi-stage compressor and multi-stage compression process

ABSTRACT

A plurality of parallel compression paths connect a suction chamber to a discharge chamber. A plurality of compression chambers are formed in each compression path. Fluid is drawn to the suction chamber and is then compressed in the compression chambers in each compression path in a plurality of compression stages. Afterward, the fluid is discharged from the discharge chamber. A first compression chamber that corresponds to a predetermined compression stage in each compression path is connected to a second compression chamber that corresponds to a subsequent compression stage in the compression path through a communication chamber. The communication chamber is provided separately for each compression path.

TECHNICAL FIELD

[0001] The present invention relates to multi-stage compression techniques that include multiple stages in which fluid is compressed to a high pressure in a plurality of compressing chambers.

BACKGROUND ART

[0002] Japanese Unexamined Patent Publication No. 10-184539 discloses a typical swash plate type two-stage compressor. The compressor includes a suction chamber, an intermediate chamber, and a discharge chamber that are formed in a housing. The suction chamber is connected to the intermediate chamber through three first compressing chambers, and the intermediate chamber is connected to the discharge chamber through three second compressing chambers. Refrigerant gas is compressed in the first compression chambers and then in the second compression chambers, in two compression stages. The double-stage compressor will now be described with reference to the schematic view of FIG. 17.

[0003] As shown in FIG. 17, refrigerant gas at suction pressure Ps′ is supplied from a suction chamber 130 to three first compressing chambers 110 a to 110 c. The refrigerant gas is then compressed in each compressing chamber 100 a to 110 c in a compression stroke. Afterward, in a discharge stroke, the refrigerant gas is compressed to intermediate pressure Pm′ (first-stage compression) and is discharged to an intermediate chamber 131. The refrigerant gas at the intermediate pressure Pm′ is then supplied from the intermediate chamber 131 to three second compression chambers 120 a to 120 c. The refrigerant gas is then compressed in each compression chamber 120 a to 120 c in a compression stroke. Afterward, in a discharge stroke, the refrigerant gas is compressed to discharge pressure Pd′ (second-stage compression) and is discharged to a discharge chamber 132.

[0004] In this compressor, the intermediate chamber 131 is located between the first compression chambers 110 a to 110 c and the second compression chambers 120 a to 120 c. Thus, one compression stage including suction, compression, and discharge is completed without being affected by the other. The arrangement is thus efficient for smoothly completing each compression stage of suction, compression, and discharge.

[0005] However, since the intermediate chamber 131 connects the three first compressing chambers 110 a to 110 c to the three second compressing chambers 120 a to 120 c, the intermediate chamber 131 is relatively large, thus enlarging the housing (for example, the diameter of the housing body is increased). Further, since pressure variation in the intermediate chamber causes pressure loss, heat loss, and the like, it is necessary to maximally suppress the pressure variation in the intermediate chamber.

[0006] Accordingly, it is an objective of the present invention to provide a multi-stage compressor and a multi-stage compression process that include a communication chamber that connects a compression chamber corresponding to a compression stage to a compression chamber corresponding to a subsequent compression stage while minimizing the size of the compressor housing.

DISCLOSURE OF THE INVENTION

[0007] To solve the aforementioned problem, a multi-stage compressor according to the present invention includes a plurality of compression paths. The compression paths connect a suction chamber that draws fluid from the exterior to a discharge chamber that discharges the fluid to the exterior. The compressing paths are parallel. Each compression path includes a plurality of compression chambers. The fluid is drawn to the suction chamber and is compressed in the compression chambers in each compression path in a plurality of compression stages. The fluid is then discharged from the discharge chamber. A first compression chamber that corresponds to a predetermined compression stage in each compression path is connected to a second compression chamber that corresponds to a subsequent compression stage in the compression path through a communication chamber. The communication chamber is provided separately for each compression path. Thus, unlike the prior-art compressor in which a common communication chamber corresponds to all compression paths, the compressor according to the present invention includes the separate communication chambers. This structure minimizes each communication chamber, thus minimizing the size of the housing.

[0008] It is preferred that the present invention is applied to a compressor that converts rotation of a swash plate to reciprocating movement of each piston for compressing fluid in each compression chamber. This structure minimizes the communication chamber that connects the first compression chamber to the second compression chamber, thus minimizing the size of the housing of the compressor.

[0009] It is also preferred that the first compression chamber is connected to the second compression chamber through the communication chamber, which is provided separately for each compression path. This structure maximally suppresses pressure variation in each communication chamber, thus preventing undesired pressure loss or heat loss caused by the pressure variation.

[0010] If a plurality of first compression chambers and a plurality of second compression chambers are located around a drive shaft and each first compression chamber is located alternately with a second compression chamber, it is preferred that the second compression chamber is located adjacent to the first compression chamber in a direction opposite to a rotational direction of the drive shaft. In this arrangement, for example, the suction stroke starts in the second compression chamber when the first compression chamber is in the discharge stroke. Accordingly, fluid is smoothly supplied from the first compression chamber to the second compression chamber through the communication chamber, thus maximally suppressing pressure variation in the communication chamber. As a result, the housing becomes smaller, and undesired pressure loss and heat loss are maximally prevented from being caused by the pressure variation in the communication chamber.

[0011] Further, it is preferred that carbon dioxide (CO₂) is used as the refrigerant gas. In this case, the pressure in each compression chamber is higher than that of compressors in which other refrigerant gases are used. This maximally suppresses the pressure variation in the communication chamber.

[0012] In addition, in the multi-stage compressor according to the present invention, fluid is supplied from the exterior to the compression paths through the suction chamber. The fluid is then compressed in a compression chamber that corresponds to a predetermined compression stage in each compression path. Next, the compressed fluid is supplied to a compression chamber that corresponds to a subsequent compression stage in the compression path through a communication chamber. The communication chamber is provided separately for each compression path. The fluid is then re-compressed to a high pressure and is supplied to the discharge chamber. The high-pressure fluid is then discharged from the discharge chamber to the exterior.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a longitudinal cross-sectional view schematically showing a main portion of a double-stage compressor of an embodiment according to the present invention;

[0014]FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;

[0015]FIG. 3 is a block diagram showing the compressor of FIG. 1;

[0016]FIG. 4 is a graph indicating an example of pressure variation in first and second compression chambers of the double-stage compressor of the same embodiment;

[0017]FIG. 5 is a schematic view showing a state of each compression chamber when a swash plate is rotated at ten degrees;

[0018]FIG. 6 is a schematic view showing a state of each compression chamber when a swash plate is rotated at 100 degrees;

[0019]FIG. 7 is a schematic view showing a state of each compression chamber when a swash plate is rotated at 190 degrees;

[0020]FIG. 8 is a schematic view showing a state of each compression chamber when a swash plate is rotated at 280 degrees;

[0021]FIG. 9 is a lateral cross-sectional view showing a double-stage compressor of another embodiment according to the present invention;

[0022]FIG. 10 is a graph indicating pressure variation in first and second compression chambers of the compressor of FIG. 9;

[0023]FIG. 11 is a schematic view showing a state of each compression chamber of the compressor of FIG. 9 when a swash plate is rotated at 10 degrees;

[0024]FIG. 12 is a schematic view showing a state of each compression chamber of the compressor of FIG. 9 when a swash plate is rotated at 100 degrees;

[0025]FIG. 13 is a schematic view showing a state of each compression chamber of the compressor of FIG. 9 when a swash plate is rotated at 190 degrees;

[0026]FIG. 14 is a schematic view showing a state of each compression chamber of the compressor of FIG. 9 when a swash plate is rotated at 280 degrees;

[0027]FIG. 15 is a schematic view showing a multi-stage compressor of another embodiment according to the present invention;

[0028]FIG. 16 is a schematic view showing a multi-stage compressor of another embodiment according to the present invention; and

[0029]FIG. 17 is a schematic view showing a prior-art double-stage compressor.

BEST MODE FOR CARRYING OUT THE INVENTION

[0030] A swash plate type double-stage compressor of an embodiment of the present invention will now be described with reference to the attached drawings. The double-stage compressor of this embodiment is used as a refrigerant compressor for a refrigerator or an air conditioner. The compressor compresses refrigerant gas (for example, carbon dioxide) in two compression stages before discharging the gas.

[0031] First, the configuration of the double-stage compressor will be described with reference to FIGS. 1 to 3. As shown in FIG. 1, a double-stage compressor 1, which is a multi-stage compressor according to the present invention, includes a front housing member 2, a cylinder block 3, a rear housing member 4, and a motor housing 5, which accommodates a motor 9. The front housing member 2, the cylinder block 3, the rear housing member 4, and the motor housing 5 are fastened together through a plurality of O-rings 2 a, 3 a, 4 a.

[0032] The motor 9 has a drive shaft 6 that is rotationally supported by a bearing 5 a in the motor housing 5 and a bearing 3 b in the cylinder block 3. The cylinder block 3 accommodates a thrust race 8 a and a belleville spring 8 b that urge a rear end of the drive shaft 6 in a forward direction. A thrust bearing 2 b is located between a swash plate 7 and the front housing member 2 and receives the force of the belleville spring 8 b.

[0033] The disk-like swash plate 7 is secured to the drive shaft 6 and is accommodated in a swash plate chamber 33 in the front housing member 2. The thrust bearing 2 b is located between the swash plate 7 and the cylinder block 3. The swash plate 7 is connected to each piston through corresponding shoes 7 a. Thus, the swash plate 7, together with the drive shaft 6, rotates in the direction indicated by the arrow 40 of FIG. 2. This reciprocates each piston in the directions indicated by the arrows 42, 44 of FIG. 1. The angle at which the swash plate 7 is inclined with respect to the drive shaft 6 is changed as necessary.

[0034] As shown in FIG. 2, a pair of first cylindrical bores 11 a, 11 b and a pair of second cylindrical bores 21 a, 21 b are formed in the cylinder block 3. The diameter of each second bore 21 a, 21 b is smaller than that of each first bore 11 a, 11 b. Each first bore 11 a, 11 b is located alternately with each second bore 21 a, 21 b. The bores 11 a, 11 b, 21 a, 21 b are parallel with one another and are spaced from adjacent bores 11 a, 11 b, 21 a, 21 b at equal angular intervals (ninety degrees). That is, the first bores 11 a, 11 b are located close to the second bores 21 a, 21 b. First pistons 12 a, 12 b are movably accommodated in the first bores 11 a, 11 b, respectively, and second pistons 22 a, 22 b are movably accommodated in the second bores 21 a, 21 b, respectively (as shown in FIGS. 5 and 11). The first bore 11 a and the first piston 12 a form a first compression chamber 10 a, and the first bore 11 b and the first piston 12 b form a first compression chamber 10 b. The second bore 21 a and the second piston 22 a form a second compression chamber 20 a, and the second bore 21 b and the second piston 22 b form a second compression chamber 20 b.

[0035] As shown in FIGS. 1 and 2, a suction port 4 b and a suction chamber 30 are formed in the rear housing member 4 and are connected to each other. The suction chamber 30 is connected to the first compression chamber 10 a through a first suction port 14 a and an associated first suction valve (not shown). The suction chamber 30 is also connected to the first compression chamber 10 b through a-first suction port 14 b and an associated first suction valve (not shown). The first compression chamber 10 a is connected to a first intermediate chamber 31 a through a first discharge port 15 a and a first discharge valve 13 a. In the same manner, the first compression chamber 10 b is connected to a second intermediate chamber 31 b through a first discharge port 15 b and a first discharge valve 13 b.

[0036] The first intermediate chamber 31 a is connected to the second compression chamber 20 a through a second suction port 24 a and an associated second valve (not shown). The second intermediate chamber 31 b is connected to the second compression chamber 20 b through a second suction port 24 b and an associated second valve (not shown). Further, the second compression chamber 20 a is connected to a discharge chamber 32 through a second discharge port 25 a and a second discharge valve 23 a. In the same manner, the second compression chamber 20 b is connected to the discharge chamber 32 through a second discharge port 25 b and a second discharge valve 23 b. The discharge chamber 32 is common for all compression paths. The discharge chamber 32 is connected to the exterior through a discharge port 4 c.

[0037] The first suction port 14 a, the first compression chamber 10 a, the first discharge port 15 a, the first intermediate chamber 31 a, the second suction port 24 a, the second compression chamber 20 a, and the second discharge port 25 a form a first compression path. Further, the first suction port 14 b, the first compression chamber lob, the first discharge port 15 b, the second intermediate chamber 31 b, the second suction port 24 b, the second compression chamber 20 b, and the second discharge port 25 b form a second compression path. The first compression path and the second compression path are parallel and are between the suction chamber 30 and the discharge chamber 32.

[0038] The first compression chamber 10 a is connected to the second compression chamber 20 a through the first intermediate chamber 31 a. The second compression chamber 20 a is adjacent to the first compression chamber 10 a in a direction opposite to the rotational direction of the drive shaft 6 (indicated by the arrow 40 of FIG. 2). In the same manner, the first compression chamber 10 b is connected to the second compression chamber 20 b through the second intermediate chamber 31 b. The second compression chamber 20 b is adjacent to the first compression chamber 10 b in the direction opposite to the rotational direction of the drive shaft 6 (indicated by the arrow 40 of FIG. 2). The first intermediate chamber 31 a and the second intermediate chamber 31 b each correspond to a communication chamber of the present invention.

[0039] The relative positions of the first discharge ports 15 a, 15 b and the associated second suction ports 24 a, 24 b are preferably determined such that the sizes of the intermediate chambers 31 a, 31 b are minimized. For example, if the distance between the first discharge port 15 a and the second suction port 24 a is minimized, each intermediate chamber 31 a, 31 b can be smaller, and the housing can be smaller.

[0040] The process for compressing refrigerant gas with the double-stage compressor 1, which has the above-described structure, will now be described with reference to FIGS. 3 to 8.

[0041] If the motor 9 rotates the drive shaft 6, the swash plate 7 rotates in the direction indicated by the arrow 40 of FIG. 2. The rotation of the swash plate 7 is converted to reciprocating movement of the first pistons 12 a, 12 b and the second pistons 22 a, 22 b. This varies the volumes of the first compression chambers 10 a, 10 b and the volumes of the second compression chambers 20 a, 20 b.

[0042] Thus, as shown in FIG. 3, refrigerant gas at suction pressure Ps is drawn to the suction chamber 30 through the suction port 4 b. The refrigerant gas then passes through the first suction ports 14 a, 14 b, which are opened by the associated first suction valves (not shown) and reaches the first compression chambers 10 a, 10 b during the corresponding suction strokes. The refrigerant gas is then compressed during the corresponding compression strokes. Subsequently, the refrigerant gas is compressed to an intermediate pressure Pm (first-stage compression) in the corresponding discharge strokes and is discharged to the intermediate chambers 31 a, 31 b through the first discharge ports 15 a, 15 b, which are opened by the first discharge valves 13 a, 13 b.

[0043] Subsequently, the refrigerant gas, which is at the intermediate chambers 31 a, 31 b flows from the intermediate chambers 31 a, 31 b to the second compression chambers 20 a, 20 b during the corresponding to a suction stroke through the second suction ports 24 a, 24 b, which are opened by the associated second suction valves (not shown). The refrigerant gas is then compressed in the corresponding compression strokes. Afterward, the refrigerant gas is further compressed to discharge pressure Pd (second-stage compression) during the corresponding discharge strokes and is discharged to the discharge chamber 32 through the second discharge ports 25 a, 25 b, which are opened by the second discharge valves 23 a, 23 b. The refrigerant gas at the discharge pressure Pd is then discharged from the discharge chamber 32 to the exterior of the compressor through the discharge port 4 c.

[0044] Next, among the four compression chambers, pressure variation in the first compression chamber 10 a and pressure variation in the second compression chamber 20 a that is connected to the first compression chamber 10 a will be described in detail with reference to FIGS. 4 to 8.

[0045] As shown in FIG. 4, the rotational angle of the swash plate 7 is defined as zero degrees when the first piston 12 a is located at its bottom dead center in the first compression chamber 10 a. In the first compression chamber 10 a, a compression stroke C1 starts from this state. Immediately before the rotational angle of the swash plate reaches 90 degrees, a discharge stroke D1 starts in the first compression chamber 10 a. The discharge stroke D1 continues until the rotational angle of the swash plate reaches approximately 180 degrees, or until the first piston 12 a reaches its top dead center. During the discharge stroke D1, pressure variation Pt is caused in the first compression chamber 10 a, as shown in FIG. 4. Pressure variation Pt is also caused in the first intermediate chamber 31 a, which is connected to the first compression chamber 10 a. Afterward, an expansion stroke E1 starts in the first compression chamber 10 a when the rotational angle of the swash plate is approximately 180 degrees. The expansion stroke E1 is then followed by a suction stroke S1, and the suction stroke S1 continues until the rotational angle of the swash plate reaches approximately 360 degrees.

[0046] Further, a discharge stroke D2 continues in the second compression chamber 20 a when the rotational angle of the swash plate increases from zero degrees to approximately 90 degrees, or until the second piston 22 a reaches its top dead center. Afterward, an expansion stroke E2 starts in the second compression chamber 20 a when the rotational angle of the swash plate is approximately 90 degrees. The expansion stroke E2 is followed by a suction stroke S2, and the suction stroke S2 continues until the rotational angle of the swash plate reaches approximately 270 degrees. When the rotational angle of the swash plate is approximately 270 degrees, the second piston 22 a reaches its bottom dead center. In this state, a compression stroke C2 starts in the second compression chamber 20 a. The compression stroke C2 then continues until the rotational angle of the swash plate reaches approximately 360 degrees.

[0047] The pressure in the first compression chamber 10 b and the pressure in the second compression chamber 20 b vary in the same manner as the pressure in the first compression chamber 10 a and the pressure in the second compression chamber 20 a. Thus, description of the pressure variation in the first compression chamber 10 b and the pressure variation in the second compression chamber 20 b are omitted.

[0048] Next, the states of each compression chamber corresponding to FIG. 4 will be described with reference to FIGS. 5 to 8. More specifically, FIGS. 5, 6, 7, and 8 each schematically show a state of each piston and the associated suction and discharge valves when the rotational angle of the swash plate 7 is 10, 100, 190, and 280 degrees, respectively.

[0049] As shown in FIG. 5, when the rotational angle of the swash plate 7 is approximately 10 degrees, the first piston 12 a and the second piston 22 a each move in the directions indicated by the arrows in the drawing (hereafter, the moving direction of each piston is indicated by a similar arrow). In this state, the first compression chamber 10 a is under the compression stroke C1, and the second compression chamber 20 a is under the discharge stroke D2. In other words, only the second discharge valve 23 a is open, and the remaining discharge and suction valves are closed.

[0050] As shown in FIG. 6, when the rotational angle of the swash plate 7 is approximately 100 degrees, the first compression chamber 10 a is under the discharge stroke D1, and the second compression chamber 20 a is under the expansion stroke E2. That is, only the first discharge valve 13 a is open, and the remaining discharge and suction valves are closed. The discharge stroke D1 continues in the first compression chamber 10 a, and the first compression chamber 10 a is connected to the first intermediate chamber 31 a, until the rotational angle of the swash plate reaches approximately 180 degrees. Thus, the pressure variation Pt (see FIG. 4) in the first compression chamber 10 a affects the first intermediate chamber 31 a. Further, the suction stroke S2 starts at a later stage of the discharge stroke D1 in the first compression chamber 10 a. Refrigerant gas is thus smoothly supplied from the first compression chamber 10 a to the second compression chamber 20 a. This reduces the pressure variation Pt to a relatively low level.

[0051] As shown in FIG. 7, when the rotational angle of the swash plate is approximately 190 degrees, the first compression chamber 10 a is under the expansion stroke E1, and the second compression chamber 20 a is under the suction stroke S2. In other words, only the associated second suction valve is open, and the remaining suction and discharge valves are closed.

[0052] As shown in FIG. 8, when the rotational angle of the swash plate is approximately 280 degrees, the first compression chamber 10 a is under the suction stroke S1, and the second compression chamber 20 a is under the compression stroke C2. In other words, only the associated first suction valve is open, and the remaining suction and discharge valves are closed.

[0053] In the compressor constructed as described, the first intermediate chamber 31 a connects the first compression chamber 10 a to the second compression chamber 20 a. Likewise, the second intermediate chamber 31 b connects the first compression chamber 10 b to the second compression chamber 20 b. In other words, each compression path includes an independent intermediate chamber. Thus, the size of each intermediate chamber 31 a, 31 b in the rear housing member 4 is minimized, as compared to the case in which the compression paths include a common intermediate chamber. This also minimizes the size of the rear housing member 4.

[0054] Further, the second compression chamber 20 a, to which the first compression chamber 10 a is connected through the first intermediate chamber 31 a, is adjacent to the first compression chamber 10 a in the direction opposite to the rotational direction of the drive shaft 6 (indicated by the arrow 40 of FIG. 2). In the same manner, the second compression chamber 20 b, to which the first compression chamber 10 b is connected through the second intermediate chamber 31 b, is adjacent to the first compression chamber 10 b in the direction opposite to the rotational direction of the drive shaft 6 (indicated by the arrow 40 of FIG. 2). Accordingly, the pressure variation in each intermediate chamber 31 a, 31 b is reduced to a relatively low level when the discharge stroke D1 continues in the first compression chambers 10 a, 10 b.

[0055] The present invention is not restricted to the above embodiment but may be applied to various other purposes and be modified in various manners. For example, the present invention may be carried out as the following embodiments that are modifications of the illustrated embodiment.

[0056] In the illustrated embodiment, the first compression chamber 10 a is connected to the second compression chamber 20 a that is located adjacent to the first compression chamber 10 a in the direction that is opposite to the rotational direction of the swash plate 7 (as indicated by the arrow 40 of FIG. 2). However, the first compression chamber 10 a may be connected to the other second compression chamber 20 b. This modification, which is a double-stage compressor of another embodiment according to the present invention, will hereafter be described with reference to FIGS. 9 to 14. Same or like reference numerals are given to parts in FIGS. 9 to 14 that are the same as or like corresponding parts in FIGS. 2 and 4 to 8.

[0057] As shown in FIG. 9, the first compression chamber 10 a is connected to the second compression chamber 20 b through the first intermediate chamber 31 a. The first compression chamber 10 b is connected to the second compression chamber 20 a through the second intermediate chamber 31 b. Regarding this arrangement of the intermediate chambers 31 a, 31 b, among the four compression chambers, pressure variation in the first compression chamber 10 a and pressure variation in the second compression chamber 20 b, which is connected to the first compression chamber 10 a, will be described in detail with reference to FIGS. 10 to 14. The phase of the second bore 21 b is offset from the phase of the first bore 11 a in the rotational direction of the swash plate by +90 degrees.

[0058] As shown in FIG. 10, the compression stroke C1 starts in the first compression chamber 10 a when the rotational angle of the swash plate is zero degrees, or when the first piston 12 a is located at its bottom dead center. The discharge stroke D1 then starts in the first compression chamber 10 a immediately before the rotational angle of the swash plate reaches 90 degrees. The discharge stroke D1 continues until the rotational angle of the swash plate reaches approximately 180 degrees, or until the first piston 12 a reaches its top dead center. In accordance with the discharge stroke D1, pressure variation Pu (>Pt) is caused in the first compression chamber 10 a and the first intermediate chamber 31 a. When the rotational angle of the swash plate reaches approximately 180 degrees, the expansion stroke E1 starts in the first compression chamber 10 a. The expansion stroke E1 is then followed by the suction stroke S1, and the suction stroke S1 continues until the rotational angle of the swash plate reaches approximately 360 degrees.

[0059] The suction stroke S2 continues in the second compression chamber 20 b when the rotational angle of the swash plate increases from zero degrees to approximately 90 degrees. When the rotational angle of the swash plate is 90 degrees, the second piston 22 b reaches its bottom dead center. The compression stroke C2 starts in the second compression chamber 20 b when the rotational angle of the swash plate is approximately 90 degrees. The compression stroke C2 continues until the rotational angle of the swash plate reaches approximately 180 degrees. When the rotational angle of the swash plate is approximately 180 degrees, the discharge stroke D2 starts in the second compression chamber 20 b. The discharge stroke D2 continues until the rotational angle of the swash plate reaches approximately 270 degrees. When the rotational angle of the swash plate is 270 degrees, the second piston 22 b reaches its top dead center. The expansion stroke E2 starts in the second compression chamber 20 b when the rotational angle of the swash plate is approximately 270 degrees. The expansion stroke E2 is then followed by the suction stroke S2.

[0060] Next, states of each compression chamber corresponding to FIG. 10 will hereafter be described with reference to FIGS. 11 to 14. The rotational angles of the swash plate 7 in FIGS. 11 to 14 correspond to those of FIGS. 5 to 8, respectively.

[0061] As shown in FIG. 11, when the rotational angle of the swash plate is approximately 10 degrees, the first compression chamber 10 a is under the compression stroke C1 and the second compression chamber 20 b is under the suction stroke S2. That is, only the associated second suction valve is open, and the remaining suction and discharge valves are closed.

[0062] As shown in FIG. 12, when the rotational angle of the swash plate is approximately 100 degrees, the first compression chamber 10 a is under the discharge stroke D1 and the second compression chamber 20 b is under the compression stroke C2. That is, only the first suction valve 13 a is open, and the remaining suction and discharge valves are closed. The discharge stroke D1 continues in the first compression chamber 10 a and the first compression chamber 10 a is connected to the first intermediate chamber 31 a, until the rotational angle of the swash plate reaches approximately 180 degrees. The pressure variation Pu (see FIG. 10) in the first compression chamber 10 a thus affects the first intermediate chamber 31 a. Further, since the second compression chamber 20 a is under the compression stroke C2 when the first compression chamber 10 a is under the discharge stroke D1, the pressure variation Pu is slightly larger than the pressure variation Pt of FIG. 4. However, as compared to the prior art compressor, this embodiment minimizes the size of the communication chambers to minimize the size of the housing, like the above-described embodiment.

[0063] As shown in FIG. 13, when the rotational angle of the swash plate is approximately 190 degrees, the first compression chamber 10 a is under the expansion stroke E1, and the second compression chamber 20 b is under the discharge stroke D2. Thus, only the second discharge valve 23 b is open, and the remaining suction and discharge valves are closed.

[0064] As shown in FIG. 14, when the rotational angle of the swash plate is approximately 280 degrees, the first compression chamber 10 a is under the suction stroke SI, and the second compression chamber 20 b is under the expansion stroke E2. Thus, only the associated first suction valve is open, and the remaining suction and discharge valves are closed.

[0065] However, as compared to this embodiment, in which the first compression chamber 10 a is connected to the second compression chamber 20 b through the first intermediate chamber 31 a, the pressure variation in each intermediate chamber is further effectively suppressed by the embodiment of FIG. 2, in which the first compression chamber 10 a is connected to the second compression chamber 20 a through the first communication chamber 31 a.

[0066] In the illustrated embodiments, the two types of compression chambers with different volumes, consisting of the first compression chambers 10 a, 10 b and the second compression chambers 20 a, 20 b, compress refrigerant gas in two compression stages. However, the numbers and types of the compression chambers are not restricted to the illustrated embodiments and may be changed as necessary. For example, the present invention may be applied to a compressor or a compression process that employs three or more types of compression chambers with different volumes for compressing refrigerant gas at three or more stages.

[0067] Further, in the illustrated embodiments, the present invention is applied to a compressor or a compression process in which the refrigerant gas is compressed through the reciprocating of the pistons. However, the present invention may be applied to other types of compressors. For example, the present invention may be applied to rotating type compressors or compression processes such as scroll types.

[0068] The multi-stage compressor may be configured as follows:

[0069] The multi-stage compressor may include a plurality of compression paths that connect a suction chamber to a discharge chamber. The compression paths are parallel. Each compression path includes a plurality of compression chambers, and each compression chamber corresponds to a compression stage. Refrigerant is thus compressed to a high pressure in a plurality of compression stages. In each compression path of this multi-stage compressor, a compression chamber N that corresponds to a compression stage N is connected to a compression chamber (N+1) that corresponds to a compression stage (N+1) through a communication chamber. The communication chamber is provided separately for each compression path. N is an integer that is smaller than the total number of the compression stages.

[0070] In this structure, each compression path has the associated communication chamber that connects the compression chamber N to the compression chamber (N+1). In other words, unlike the prior art compressor that has a common communication chamber for the compression chambers, the compressor includes the separate communication chambers. This structure minimizes each communication chamber, thus minimizing the housing.

[0071] Further, the compressor may be configured as follows:

[0072] The multi-stage compressor may include a plurality of compression lines that connect a suction chamber to a discharge chamber. The compression lines are parallel. Each compression line includes a plurality of compression chambers, and each compression chamber corresponds to a compression stage. Refrigerant is thus compressed to a high pressure in a plurality of compression stages. The compression lines are divided into a plurality of compression paths. In at least one compression path, one or more compression chambers N, each of which correspond to a compression stage N, are connected to one or more compression chambers (N+1), each of which correspond to a compression stage (N+1), through a communication chamber. A communication chamber is provided separately for each compression path. N is an integer that is smaller than the total number of the compression stages. Further, each compression path may include one or more compression lines.

[0073] In this structure, the compression lines are appropriately divided into the compression paths. The communication chamber that connects one or more compression chambers N to one or more compression chambers (N+1) in at least one compression path is provided separately for each compression path. In other words, the compressor includes separate communication chambers, unlike the prior art compressor that has a common communication chamber for the compression chambers. This structure minimizes the size of each communication chamber, thus minimizing the size of the housing.

[0074] This multi-stage compressor will now be described with reference to FIGS. 15 and 16.

[0075] As shown in FIG. 15, the multi-stage compressor includes three compression lines. The compression lines are divided into two compression paths. More specifically, a first compression path includes the two compression lines that are indicated in an upper portion of FIG. 15. A second compression path includes the compression line that is indicated in a lower portion of FIG. 15. In the first compression path, a compression chamber N₁ and a compression chamber N₂, are connected to a compression chamber (N+1)₁ and a compression chamber (N+2)₂, through a first communication chamber M₁. Further, in the second compression path, a compression chamber N₃, is connected to a compression chamber (N+1)₃, through a second communication chamber M₂. That is, the multi-stage compressor of FIG. 15 has separate communication chambers M₁, M₂, each of which corresponds to one compression path.

[0076] Alternatively, as shown in FIG. 16, the multi-stage compressor includes four compression lines. The compression lines are divided into two compression paths. More specifically, a first compression path includes the two compression lines that are indicated in an upper portion of FIG. 16. A second compression path includes the two compression lines that are indicated in a lower portion of FIG. 16. In the first compression path, a compression chamber N₁ and a compression chamber N₂, are connected to a compression chamber (N+1)₁ and a compression chamber (N+2)₂, through a first communication chamber M₁. Further, in the second compression path, a compression chamber N₃ and a compression chamber N₄, are connected to a compression chamber (N+1)₃ and a compression chamber (N+1)₄, through a second communication chamber M₂. That is, the multi-stage compressor of FIG. 16 has the separate communication chambers M₁, M₂, each of which corresponds to one compression path.

[0077] As described, the three compression lines of FIG. 15 are divided into the two compression paths, and the four compression lines of FIG. 16 are divided into the two compression paths. However, the total number of the compression lines, the total number of the compression paths, or the total number of the compression lines that form each compression path are not restricted to the above description but may be changed as necessary. For example, four compression lines may be divided into three compression paths. In this case, a first compression path includes a pair of compression lines, and second and third compression paths each include a compression line.

[0078] The technical terms used in this application are defined as follows.

[0079] (1) The term “multi-stage compressor” includes not only reciprocation type compressors that compress refrigerant through movement of a piston but also other types of compressors such as rotating type compressors, for example, scroll type compressors.

[0080] (2) The term “refrigerant gas” includes not only carbon dioxide (CO₂) but also various fluids such as ethylene (C₂H₄), ethane (C₂H₆), diborane (B₂H₆), and liquid nitrogen.

[0081] (3) The term “compression path” includes a compression path in which each compression stage corresponds to a plurality of compression chambers. 

1. A multi-stage compressor including a plurality of compression paths, which connect a suction chamber that draws a fluid from the exterior to a discharge chamber that discharges the fluid to the exterior, the compression paths being parallel, each compression path including a plurality of compression chambers, wherein the fluid drawn to the suction chamber is compressed in the compression chambers of each compression path in a plurality of compression stages and is discharged from the discharge chamber, the compressor being characterized in that: a first compression chamber that corresponds to a predetermined compression stage in each compression path is connected to a second compression chamber that corresponds to a subsequent compression stage in the compression path through a communication chamber, which is provided separately for each compression path.
 2. The multi-stage compressor as set forth in claim 1 further comprising: a drive shaft, a swash plate that rotates integrally with the drive shaft, and a piston movably located in each compression chamber for reciprocating movement in accordance with the rotation of the swash plate.
 3. The multi-stage compressor as set forth in claim 2, wherein: the compression chambers are located alternately around the drive shaft.
 4. The multi-stage compressor as set forth in claim 3, wherein the second compression chamber is located adjacent to the first compression chamber in a direction opposite to the rotational direction of the drive shaft.
 5. The multi-stage compressor as set forth in any one of claims 1 to 4, wherein the fluid is carbon dioxide.
 6. A multi-stage compressor including a plurality of compression paths that connect a suction chamber to a discharge chamber, the compression paths being parallel, the compressor compressing a fluid to a high pressure in a plurality of compression chambers in each compressing path in a plurality of compression stages, each compression chamber corresponding to one compression stage, wherein: a compression chamber N that corresponds to a compression stage N in each compression path is connected to a compression chamber (N+1) that corresponds to a compression stage (N+1) in the compression path through a communication chamber, which is provided separately for each compression path, and N is an integer.
 7. A multi-stage compressor including a plurality of compression lines that connect a suction chamber to a discharge chamber, the compression lines being parallel, the compressor compressing a fluid to a high pressure in a plurality of compression chambers in each compression line in a plurality of compression stages, each compression chamber corresponding to one compression stage, the compressor comprising: a plurality of compression paths, which are formed by the compression lines, wherein one or more compression chambers N that correspond to a compression stage N in at least one compression path is connected to one or more compression chambers (N+1) that correspond to a compression stage (N+1) in the compression path through a communication chamber, which is provided separately for each compression path.
 8. A multi-stage compression process comprising: supplying a fluid from the exterior to a plurality of compression paths through a suction chamber; compressing the fluid in a compressing chamber that corresponds to a predetermined compression stage in each compression path; supplying the compressed fluid to a compression chamber that corresponds to a subsequent compression stage through a communication chamber, which is provided separately for each compression path; compressing the supplied fluid to a high pressure; and supplying the high pressure fluid to a discharge chamber before discharging the fluid from the discharge chamber to the exterior.
 9. The multi-stage compression process as set forth in claim 8, wherein the fluid is compressed through reciprocating movement of a piston. 